Rep. Sean Duffy’s constituents and colleagues should be ashamed of him.

In an interview on CNN on Tuesday, the Wisconsin Republican applauded the “good things that came from” a white supremacist murdering nine black worshippers at a church in Charleston, South Carolina, in 2015.

“Nikki Haley took down the Confederate flag,” he chirped with excitement. “That was great!” Never mind that Duffy has voted to defend the right of ROTCs to fly the battle banner of traitors.

Then, he tried to use a former colleague as a prop so that he could blame liberalism for a shooting rampage in Tucson, Arizona, in early 2011. “Look at Gabby Giffords,” Duffy said. “The Marxist who took her life, a leftist guy, and now you see violence and terror in the streets all across America, burning and beating people with Donald Trump hats.”

Giffords is alive. She took a bullet to the brain and survived it. Since then, she’s worked to enhance gun-control measures in ways far more measured than some of her fellow Democrats. The guy who shot her, Jared Loughner, was mentally ill and had access to firearms. To the extent that he had a definable political ideology, it wasn’t liberal; it was anti-government and tilted toward right-wing conspiracy theories. But it would be foolish to attribute his killing spree — which, again, did not claim Giffords’ life — to any sort of coherent political belief system.

“Congressman Duffy doesn’t know the facts around the Tucson shooting nor the Charleston shooting,” Peter Ambler, executive director of Giffords’ Americans for Responsible Solutions told me in an e-mail. “Gabby is using her second chance at life to address the 30,000 people who die tragically from guns every year in America.”

And, for what it’s worth, Trump is the leader who encourages his followers to commit acts of violence in the name of politics.

You might think Duffy was done saying dumb things on national television. But you’d be wrong. He went for a hat trick. When CNN’s Alisyn Camerota pressed him to explain why he kept describing terrorist attacks by white supremacists against minorities as one-off events, this is what he said: “Can we vet that? How should we vet that to keep ourselves safe.” He then offered to help find a solution to that before reverting to “So, let’s crack down on ISIS.”

But it’s clear that in Duffy’s book, there’s no existing pattern to violence by white supremacists against people of color. He must have forgotten the white hatemonger who massacred six people at a Sikh temple in Oak Creek, Wisconsin, in 2012 and the resolution he co-sponsored condemning that attack.

What would possess Duffy to make such offensive and ignorant statements back-to-back-to-back? His zeal in arguing for President Trump’s executive order on travel to the U.S.— the one that started out as a Muslim ban — and against the idea that right-wing extremists in the U.S. can be terrorists. He’s so eager to impress the Donald that he’ll say just about anything. CNN knows that. Give him a few minutes on air and he’ll blunder into at least one statement deserving of derision and ridicule. There’s definitely a pattern there, going back years.

On Tuesday, it took him just five minutes to say three of the most memorably reprehensible things any member of Congress has uttered in the 15-plus years since I first started writing about Capitol Hill — and, trust me, that’s saying a whole hell of a lot.

The irony: It’s taken Duffy only six years in Washington to become so detached from reality and such a terrible television guest after having made his name on a TV show called “The Real World.” Whatever planet he’s on, the air is suffused with the aroma of power.

Now, he’s focused mostly on figuring out how to become a big shot — and the answer right now is proving his fealty to Trump by emulating the president on TV. And, of course, he also seems to be trying to protect his northwestern Wisconsin district from the terrorists who are crawling all over each other to migrate there from … Duluth, the upper peninsula of Michigan or the middle of Lake Superior.

For 58 years, the 7th District of Wisconsin was represented by two of the most capable and thoughtful members of Congress, Republican Mel Laird and Democrat Dave Obey. Between them, they shaped major debates over war and peace, funneled money back home from the House Appropriations Committee, and gave their constituents representation of which they could always be proud.

It’s possible that no district has ever voted for such a lightweight after having sent such powerhouses to Congress for so long. Democrats will probably lose there in 2018, but they should make sure to field a quality candidate just because Duffy’s constituents deserve a decent alternative. Heck, a smart Republican should primary him just on the basis that voters might want a legislator who doesn’t embarrass them.

At the very least, Duffy owes his constituents an apology. And he owes fellow Republicans who have to live with his off-the-wall commentary an apology. More important, he should apologize to Giffords and the families of the Tucson and Charleston shooting victims who died.